These studies are designed to assess prospectively the long-term sequelae of bacterial meningitis experienced by children in whom the etiologic diagnosis has been made rapidly and whose treatment has been provided uniformly according to a protocol supervised by specialists in pediatric infectious diseases and neurology. Antigenic stimuli provided by Hemophilus influenzae disease are being quantitated and correlated with antibody responses in the same children in an attempt to gain information which may be important in the ultimate development and application of H. influenzae vaccine for the prevention of H. influenzae meningitis in infancy and childhood. Specific studies will also be directed towards an evaluation of the interaction of H. influenzae type b and it's capsular polysaccharide with antibody and polymorphonuclear leukocytes in pediatric patients. An attempt is being made to determine the importance of cellular adherence in the response of children of various ages to H. influenzae infection. Investigation of the role of normal anaerobic flora in the nasopharynx and gastrointestinal tract in the production of cross-reactive immunity to H. influenzae has been undertaken.